As The Battle For Basra Rages, Iran`s Plans Leave U.s. Puzzled

WASHINGTON -- With carnage reminiscent of the trench warfare during World War I, the battle for the Iraqi port city of Basra, at the head of the Persian Gulf, is about to go into its second month.

Both Iraq and Iran made what seemed to be exaggerated reports of enemy casualties last week, with Baghdad citing 100,000 Iranian casualties and Tehran saying 30,000 Iraqis had been killed or wounded. United States Defense Intelligence Agency estimates were lower but still dramatic: 50,000 casualties for Iran and 10,000 to 20,000 for Iraq.

Last week, President Reagan condemned Iran`s seizure of Iraqi territory and called the war a threat to ``American strategic interests.``

Iran`s plans and the likely outcome of the battle remained a puzzle to American intelligence authorities. Iran has long promised a ``final offensive`` by late March but now says it has not begun. Some analysts say the Iranians may be content, for now, to hold the ground they have captured.

They have made small gains south of Basra near Fish Lake, which runs perpendicular to the strategic Shatt al-Arab waterway connecting Basra with the Persian Gulf. They have also gained footholds on some islands in the Shatt but have not been able to cross it.

Iraqi counterattacks, including one using elite Presidential Guards, have failed. Baghdad apparently was forced to concede Iran`s gains and try to use its superior artillery and airpower to bar further advances. Military experts doubt Iran can capture Basra but say that constant shelling can insure that the town remains unlivable.

The State Department publicly played down Iran`s latest gains and implied that the battle was about over. But military intelligence sources said the lull may be a breather while the Iranians are resupplied and reinforced. Of the estimated 200,000 Iranians available, they said, only about 60,000 have been fighting. The degree to which munitions and equipment are available to sustain Iran`s attacks is not precisely known. But its main problem, military sources say, has not been availability so much as logistics, getting supplies to the front.

American intelligence analysts noted that the Iranians were successful last week in moving men and supplies at night, despite fierce Iraqi artillery and air attacks.

But Iran also has had difficulty in the past controlling and coordinating its units, and this has been attributed to lack of communications and professional competence. Iraq has indicated that the recent fighting has involved only units of the Iranian Revolutionary Guards, who, American sources say, are emerging as Iran`s new army.

The regulars held over from the shah`s time are increasingly relegated to static defensive duty. The Revolutionary Guards reportedly have taken on the organization and trappings of a conventional army. They are showing increased military sophistication, leading American analysts to believe they may now be able to overcome logistic and control problems and sustain their attacks.

Analysts note that Iraq has reinforced its southern front with forces from regions as far north as Mandali, along the border east of Baghdad. The Basra attack, they say, may be a diversion, and the main Iranian attack may be launched farther north. Intelligence sources say Iran has substantial forces in the Ahvaz-Dezful area, north of Basra, and near Mandali, where clashes have already occurred.

While the fighting raged around Basra last week, both sides launched air attacks and used Soviet-made ``Scud`` surface-to-surface missiles. Iraq reportedly launched 14 Scuds, and the Iranians hit Baghdad with six of them. Exploiting its superiority in the air, Iraq bombed Iranian cities, including Tehran and the holy city of Qum. Iran said about 1,700 civilians have been killed and 6,000 wounded in 29 cities.

There were also new maritime developments last week. Iranians launched Italian-made ``Sea Killer`` missiles at night from warships near the Strait of Hormuz, at the entrance to the Persian Gulf -- attacking neutral shipping doing business with Kuwait, a major transshipment point for war materials bound for Iraq. Three oil tankers were damaged in the territorial waters of Oman and the United Arab Emirates. And the Soviet Union sent a Krivak-class frigate into the Gulf for the first time, escorting four Soviet merchant ships reportedly carrying arms for Iraq.

The intensity of the fighting has strained both sides, yet both boast of high morale and unflagging determination. The claims are difficult to assess because neither country has let outsiders watch the battles. Iraq has a smaller population to draw upon for military service. Its army includes a large number of Shiite Moslems, who might be sympathetic to Iran`s fundamentalist revolution. Consequently, Iraq has always been reluctant to risk heavy casualties by counterattacking on the ground.

Iraq`s ability to withstand losses may determine the outcome. Experts do not discount the possibility that Iraq`s military leaders may decide one day that their president, Saddam Hussein, is the main obstacle to ending the war and look for a way to remove him.